Which scan type performs a TCP three-way handshake?

Which scan type performs a TCP three-way handshake?

• A. -sS
• B. -sU
• C. -sA
• D. -sT

Answer: (D)

A TCP three-way handshake is how a full TCP connection is established: SYN from the initiator, SYN-ACK from the target, and ACK to finish. The scan that performs this handshake uses the system’s connect() call to complete a TCP connection to the target port, so the handshake happens as part of establishing that connection. That is why this scan type is the one that actually carries out the three-way handshake. In contrast, a SYN scan sends only the initial SYN and doesn’t complete the handshake, a UDP scan uses UDP rather than TCP, and an ACK scan sends ACKs to probe firewall behavior without forming a full connection.

A TCP three-way handshake is how a full TCP connection is established: SYN from the initiator, SYN-ACK from the target, and ACK to finish. The scan that performs this handshake uses the system’s connect() call to complete a TCP connection to the target port, so the handshake happens as part of establishing that connection. That is why this scan type is the one that actually carries out the three-way handshake. In contrast, a SYN scan sends only the initial SYN and doesn’t complete the handshake, a UDP scan uses UDP rather than TCP, and an ACK scan sends ACKs to probe firewall behavior without forming a full connection.